hot-dip zinc coating

Zinc is a natural metallic chemical element. It is present in our natural environment, in the air, soil and water reservoirs. Zinc is not harmful to the environment; it is even a necessary element for living organisms. Zinc can be recycled.

The hot-dip zinc coating (plating) known as zinc coating by immersion is one of the most efficient methods for steel structure rustproof protection. The process consists in submerging steel objects in a tank filled with melted zinc alloy at a temperature of 445 - 455 ^oC.

Prior to submerging, the structure (object) is prepared in the following stages.

forming charge                                                                  chemical degreasing

rinsing                                                                 acid pickling

rinsing                                                                 flux coating

drying                                                                 The last stage is cooling in water at ambient temperature.

Objects taken out from slings are mechanically cleaned to remove zinc sagging. The coat obtained features high mechanical resistance and aesthetic appearance. The thickness of zinc layer depends on the thickness of item to be plated, which is presented in the table below.

Structure component thickness in mm	Minimum zinc layer thickness in µm
do 1	50
1 - 3	55
3 - 6	70
over 6	85

Average zinc loss in a structure being in use ranges from 1 - 2 µm per year (for use under non-aggressive conditions). Therefore, the average working life of zinc coats is 30 years, but it can reach even 100 years. The rust protective zinc coat does not require any maintenance.

Alternative methods of providing rust protection, such as painting, are cheaper but their life is much shorter and does not exceed 5 to 10 years.

The cost of cleaning a paint-coated and rusted structure e.g. by sand blasting is comparable to zinc plating!